Case-hardening



UNITED, STATES PATENT OFFICE.

SAMUEL WHYTE, 0F REDHILL, ENGLAND.

CASE-HARDENING.

1 ,345 ,o5o. No Drawing.

To all whom it may concern.

Be it known that I, SAMUEL WHY'rn, $0., a subject of the King of GreatBrltaln and Ireland, and residing at ll Woodlands road, Redhill, in thecounty of Surrey, England, metallurgist, have invented certain new anduseful Improvements Relating to Case-Hardening, of which the followingis a specification.

This invention relates to a new method of producing casings on finishedor partly finished articles of iron, steel, alloy steels, or the like.

The invention consists broadly in a new method of producing iron-carbonalloys or alloys of iron alloyed with other metals as a fused casing onthe surface of finished or partly finished articles by heating them to asuitable temperature with borax'in the presence of carbon preferably inthe form of graphite.

-The invention further consists in employing an alternating or directelectric current to facilitate the production ofthe case.

The invention also consists in employing a direct current and makin thework the anode or the cathode accordlng as rounded and it is preferredto pass a current 0f'air through the bath.

The depth and nature of the altered superficial layer or casing dependson the time of treatment and the tem erature of the bath, as also ofcourse upon t e constitution of the original metal.- The casing as it isformed is very fluid and tends to flow off. If after 'a slight uniformcasing the article is placed in a cooler part of the bath or transferredto a bath of a lower temperature a diffusion of carbon would take placeand give a deeper case. By controlling the temperature of the bath andthe time of treatment" in relation to the constitution of the originalmaterial, the depth and composition of the @casing'. can be regulated.The

temperatur'e of the-bath may conveniently be about T200 to '1400 .C. Thepresence of Specification of Letters Patent. Patented June 29, 1920.

Application filed October 10, 1917. Serial'No. 196,837. f

alloys of higher carbon content have lower melting points.

This process can be usefully applied in many ways. For example, anengine cylinder may be produced of steel, yet having a working surfaceof a white'iron. Other applications of this invention are the casing oftubes or vessels, where the strength of steel is required with thecorrosion or erosion resisting properties of white cast iron, or againthe casing of turbine blades or fastening devices such as screws ornuts.

Where a thick coating is desired cast iron may be melted in the bottomof the crucible with a layer of borax or the like on the top, andarticles may be coated rapidly with the required casing. by dipping. Theiron has its silicon rapidly eliminated by heating with the borax, andwhere sufficient carbon is used and time given the metal bath is readilyconverted into white iron of nearly constant carbon content containingabout- 2.7% of carbon; but the treatment maybe stopped at an earlierpoint with a smaller carbon content if desired. r

The articles to be coated become cleaned by the borax bath which issufiiciently deep for this purpose.-

By dippingin the metal a coating of the desired depthcanbe obtained.

When desired metals which alloy Wlth the iron carbon alloy may beintroduced into the metal bath, e. 9. copper, nickel, cobalt, tungsten,chromium, so that they will be introduced into the coating.

It will be seen that other arrangements may be made in relation to theshape, and

size of the articleto be cased, the essential feature being the raisingof the article to be treated to the reaction temperature in contact withthe molten borax and in the presence of carbon.

In carrying this invention into effect in another form, an electriccurrent is applied to the bath in the formation of the casing,preferably with the work as one electrode.

In this way the casing is more rapidly produced.

When thearticle to'be treated is made the anode, the casing produced hasa hi h carbon content (probably iron carbid Fe fi It is correspondinglyhard and microscopi call is of single constituent. The" corners of t earticleare rather more rapidly acted upon, and become rounded. If thearticle be madethe; cathode, a casing of lower carbon content isobtained (about eutectoi d composition), and the original sharpness ofthe corners is not affected. An alternating current may be employed ifdesired.

Further one or both of the electrodes may be of carbon or of iron. Wherean iron anode is used and the article is the other electrode, I findthat the case has a duplex structure which appears to be the eutectic ofwhite iron.

- In one example I have coated a rectangular plate of steel of 500 sq.cms. surface with a case about 7/ 1000ths of an inch thick in '8minutes, using the plate as the negative electrode, and employing acurrent of 50 amperes at 15 volts. Where the'work is a negativeelectrode under the conditions I' have worked, the limit of the carboncontent of the casing appears to be about .9%, whereas if the work bethe positive electrode then the limit appears to be the for- -mation ofthe single constituent Fe c.

This property may be employed} conveniently to enable any desired carboncontent to be obtained in the case.

In another example, therefore, I employed a similar plate to that abovereferred to, but

coupled the plate for five minutes as the negative pole and for threeminutes as the positive pole with the same current and voltage asbefore. The casing thus obtained was about 5 /1000ths of an inch thick.

Having now described myinvention, what I claim as new and desire tosecure I by Letters Patent is 1. The method which consists in submittingarticles of iron or steel to the action of a bath of molten borax in thepresence of carbon and at such temperature of the bath and for such timeof treatment. that a casing of high carbon-iron (white iron) is formedon the article.

2. In a process according to claim 1, the application of an electriccurrent to the bath with the article to be coated as an electrode.

3. In a process according to claim 1, the.

' In testimony whereof I have signed my name to this specification.

' SAMUEL W'HYTE.

